1. Field of the Invention
This invention relates to the stabilization of aqueous solutions containing active chlorine to reduce the loss of the active chlorine upon exposure to ultraviolet light or by contact with metals.
2. Description of the Prior Art
Various sources of active chlorine have been widely used to kill pathogenic bacteria and to prevent their growth in potable water supplies and in swimming pools, and in general in sterilizing solutions. A serious drawback in the use of active chlorine as a bactericide is that the active chlorine in an aqueous solution is subject to rapid decomposition upon exposure to ultraviolet light, for example, upon exposure to sunlight, and also when in contact with metals such as iron, copper or aluminum which may be present in the equipment handling the solution. The rate of decomposition is particularly high in the very dilute solutions used in potable water supplies and swimming pools. In swimming pools, for example, where it is desired to maintain an active chlorine content of about 0.4 to 5.0 parts per million (ppm), it is generally necessary to add many times this amount of active chlorine in the course of an ordinary sunny day. The decomposition of the active chlorine also results in a drop in the desired pH level of the aqueous solution, thus requiring a pH adjustment with an alkali.
In U.S. Pat. No. 2,988,471, issued to Robert J. Fuchs et al on June 13, 1961, a method is disclosed for stabilizing aqueous solutions containing active chlorine against decomposition by ultraviolet light and by contact with iron and copper. The method disclosed therein involves adding to the solution cyanuric acid, ammelide or a salt of such compounds. The loss of active chlorine is substantially reduced when such materials are added to the solution in a weight concentration, expressed as the acid, which is greater than the weight concentration of available chlorine in the solution. The use of cyanuric acid to substantially reduce the loss of active chlorine in aqueous systems exposed to sunlight, for example, in swimming pools, has received wide commercial acceptance.
Although satisfactory results are achieved with the teachings of the prior art, those skilled in the art are interested in alternative materials which may be employed to stabilize the active chlorine in aqueous systems against decomposition upon exposure to ultraviolet light and/or when in contact with metals. Compounds which are easy to prepare and which offer cost/performance advantages would be of particular interest.
The object of the present invention is to provide a method for reducing the loss of active chlorine in aqueous systems upon exposure to ultraviolet light or by contact with metals such as iron, copper and aluminum employing compounds heretofore not disclosed for such use.
These and other objects will become apparent from the following detailed description.